I have two view controllers inside a UIPageViewController. I need to get all view controllers inside the UIPageViewController to call methods inside them, but it always returns a single page only (either the first page or the second page).
The code is below for convenience:
if let viewControllers: [UIViewController] = self.viewControllers {
print(viewControllers)
for controller in viewControllers {
if let firstController: FirstViewController = controller as? FirstViewController {
//Call something
}
if let secondController: SecondViewController = controller as? SecondViewController {
//Call something
}
}
}
In fact, it returns only the visible view controller inside the page controller.
This is intended behaviour.
In a simple UIPageViewController, this array will only return the currently visible view controller(s), which is usually just one view controller.
Keep in mind that UIPageViewController heavily caches and reuses controllers, just like a UITableViewController would. You may want to reflect changes in another way.
Related
I want to pass data from a view controller to tabbar controller, and then from this tab bar controller to its view controller with using their class. I succeeded to transfer from view controller to tabbar controller using segue. However, I cannot transfer data from tabbar controller to its one of the view controller.
Any idea/documentation will be appreciated. Here is the screenshot about what I want to do from xcode
screenshot-xcode
Take a look at the documentation for the tab bar controller, in particular the viewControllers property.
That property is an array of UIViewControllers, in the order they appear in the tab bar, so you can pick the one you need (viewControllers[0] from your screen shot), cast it to your specific view controller subclass and then pass it your data.
At last, I am able to solve the issue, many thanks to the answer. Here is the detailed explanation for beginners like me:
This is the source controller class, which is a tabbar controller and it transfers the data:
class SourceTC: UITabBarController {
var dataTransferFrom = "transfer this string"
override func viewDidLoad() {
super.viewDidLoad()
let finalVC = self.viewControllers![0] as! DestinationVC //first view controller in the tabbar
finalVC.dataTransferTo = dataTransferFrom
}
}
and this is the destination controller class, which is a view controller under tabbar controller and it gets the transferred data:
class DestinationVC: UIViewController {
var dataTransferTo = ""
override func viewDidLoad() {
super.viewDidLoad()
print(dataTransferTo)
}
}
I got an PageViewController which loads two "child "ViewControllers in order to let the user "swipe" through them. I don't want this swipe gesture , but instead I want to have a function inside my ViewController which allows me to use setViewControllers in the PageViewController.
I tried using protocols but even that didn't work out.
I would realy appreciate any help or suggestions on how I could accomplish that. Thanks!
To access setViewControllers from your child view controllers, you will need your child view controllers to be aware of their parent PageViewController. To do so, start by making a Protocol (I know you've said you've tried Protocols, but please please see my method through). This Protocol will ensure that every child view controller has a reference to the parent PageViewController.
protocol PageObservation: class {
func getParentPageViewController(parentRef: PageViewController)
}
Ensure that your child view controllers adhere to the PageObservation Protocol.
class Child1ViewController: UIViewController, PageObservation {
var parentPageViewController: PageViewController!
func getParentPageViewController(parentRef: PageViewController) {
parentPageViewController = parentRef
}
}
class Child2ViewController: UIViewController, PageObservation {
var parentPageViewController: PageViewController!
func getParentPageViewController(parentRef: PageViewController) {
parentPageViewController = parentRef
}
}
In your PageViewController, as you create each child view controller, cast them to the PageObservation type and pass a reference of the parent PageViewController. I use an array called orderViewControllers to create my pages. My UIPageViewControllerDataSource delegate methods uses it to know which pages to load but that is irrelevant to this example, I just thought I'd let you know in case you have a different way of creating your pages.
class PageViewController: UIPageViewController {
var orderedViewControllers: [UIViewController] = []
//creating child 1
//i am using storyboard to create the child view controllers, I have given them the identifiers Child1ViewController and Child2ViewController respectively
let child1ViewController = UIStoryboard(name: "Main", bundle: nil) .
instantiateViewController(withIdentifier: "Child1ViewController")
let child1WithParent = child1ViewController as! PageObservation
child1WithParent.getParentPageViewController(parentRef: self)
orderedViewControllers.append(child1ViewController)
//creating child 2
let child2ViewController = UIStoryboard(name: "Main", bundle: nil) .
instantiateViewController(withIdentifier: "Child2ViewController")
let child2WithParent = child2ViewController as! PageObservation
child2WithParent.getParentPageViewController(parentRef: self)
orderedViewControllers.append(child2ViewController)
}
Now inside your child view controllers, you have access to setViewControllers. For example, if I want to call setViewControllers in the child1ViewController, I have created a func called accessSetViewControllers() where I access the setViewControllers:
class Child1ViewController: UIViewController, PageObservation {
var parentPageViewController: PageViewController!
func getParentPageViewController(parentRef: PageViewController) {
parentPageViewController = parentRef
}
func accessSetViewControllers() {
parentPageViewController.setViewControllers( //do what you need )
}
}
On a side note, despite what other answers above have said, you can set dataSource to whatever you like. I sometimes set dataSource to nil to prevent the user from swiping away from a screen before doing something and then add the dataSource back to allow them to continue swiping.
Don't set dataSource. When it's nil, then gestures won't work.
https://developer.apple.com/reference/uikit/uipageviewcontroller
When defining a page view controller interface, you can provide the content view controllers one at a time (or two at a time, depending upon the spine position and double-sided state) or as-needed using a data source. When providing content view controllers one at a time, you use the setViewControllers(_:direction:animated:completion:) method to set the current content view controllers. To support gesture-based navigation, you must provide your view controllers using a data source object.
Simplistic approach... remove the inbuilt gesture recogniser in viewDidLoad of pageViewController:
for view in self.pageViewController!.view.subviews {
if let subView = view as? UIScrollView {
subView.scrollEnabled = false
}
}
Then add your own gesture below it. i just happened to be working with double tap at the moment but you could make it swipe left, swipe right easy enough:
let doubleTap: UITapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(didDoubleTap))
doubleTap.numberOfTapsRequired = 2
doubleTap.delaysTouchesBegan = true
self.addGestureRecognizer(doubleTap)
and the gesture function with your code:
func didDoubleTap(gesture: UITapGestureRecognizer) {
//... stuff
}
fileprivate func test() {
guard let w = self.view.window else {
print("no window")
return
}
guard let rootvc = w.rootViewController as? UINavigationController else {
print("no rootvc")
return
}
for vc in rootvc.childViewControllers {
print("CHILD \(vc)")
}
for vc in rootvc.viewControllers {
print("VC \(vc)")
}
}
the code above shows the same. But whats the difference between childViewControllers and viewControllers ?
According to documentation:
public var childViewControllers: [UIViewController] { get }
childViewControllers: An array of view controllers that are children of the current view controller. (read-only). This property does not include any presented view controllers. This property is only intended to be read by an implementation of a custom container view controller.
var viewControllers: [UIViewController] { get set }
viewControllers: The view controllers currently on the navigation stack.
NOTE: A ViewController also have childViewControllers property. but viewControllers property defined in UINavigationController.
ViewControllers are The view controllers currently on the navigation stack. Where ChildViewControllers are An array of view controllers that are children of the current view controller.
The root view controller is at index 0 in the array, the back view controller is at index n-2, and the top controller is at index n-1, where n is the number of items in the array.
Assigning a new array of view controllers to this property is equivalent to calling the setViewControllers:animated: method with the animated parameter set to false.
ChildViewControllers property does not include any presented view controllers. This property is only intended to be read by an implementation of a custom container view controller.
You can easily get description about it by Alt + Click on syntax!!
I need a way to make UIPageViewController reuse controllers to save memory, because I have a huge number of pages to show!
I did the basic implementation of the UIPageViewController but couldn't manage to make controller reusable, please advice!
To solve this problem in my current project, I cache all view controllers that are created as pages for the UIPageViewController in a Set. Whenever the UIPageViewController requests a new view controller from its data source, I filter out an unused from that cache by checking the parentViewController property; if no unused view controller is available, a new one is created.
My setup of the UIPageViewController and the cache looks similar to this:
class MyPageViewController: UIPageViewController {
private var reusableViewControllers = Set<MyViewController>()
init() {
super.init(/* ... */)
self.dataSource = self
let initialViewController = self.unusedViewController()
// Configure the initial view controller
// ...
self.setViewControllers([ initialViewController ],
direction: .Forward,
animated: false,
completion: nil)
}
// This function returns an unused view controller from the cache
// or creates and returns a new one
private func unusedViewController() -> MyViewController {
let unusedViewControllers = reusableViewControllers.filter { $0.parentViewController == nil }
if let someUnusedViewController = unusedViewControllers.last {
return someUnusedViewController
} else {
let newViewController = MyViewController()
reusableViewControllers.insert(newViewController)
return newViewController
}
}
}
The data source uses the same function to obtain an unused view controller:
extension MyPageViewController: UIPageViewControllerDataSource {
func pageViewController(pageViewController: UIPageViewController,
viewControllerAfterViewController viewController: UIViewController) -> UIViewController? {
let nextViewController = unusedViewController()
// Configure the next view controller for display
// ...
return nextViewController
}
}
You could use ACReuseQueue to achieve what you want. It provides a queue for reusing your view controllers. You can use the UIPageViewController data source methods to dequeue a VC from the reuse queue. The tricky part is to know when to put them back in the reuse queue. UIPageViewController does not provide any method to know when this happens, but there is a way. UIPageViewController is a container VC that adds and removes its child view controllers using the VC containment APIs.
Your VC will receive didMoveToParentViewController: with nil as the argument if it is being removed from the UIPageViewController. Use this method to add yourself back to the queue.
I have been trying to pop my view controller to one of previous view controllers in my view stack. Assume that, There are firstVC, secondVC, thirdVC and fourthVC viewcontrollers in my view stack. The current view controller is fourth one, and there is a tableview in fourthVC. If user delete all the rows in tableview, I should direct the user to secondVC. I had an idea that I would create another navigationcontroller and present it with presentViewController command. However, this is not a solution for my problem. Because I thougt that a navigation problem appears for this case. How can I find best solution for this case ?
Thank you for your answers,
Best regards
Instead of doing a generic popViewControllerAnimated: call, use popToViewController:animated:. You could detect if the user has deleted all of the rows in which case, do something like this (otherwise just pop one view controller):
let viewControllers: [UIViewController] = self.navigationController!.viewControllers as [UIViewController];
self.navigationController!.popToViewController(viewControllers[viewControllers.count - 2], animated: true);
If you want to pop to a specific view control and dont know the count to go back you can use this:
let viewControllers: [UIViewController] = self.navigationController!.viewControllers as! [UIViewController];
for aViewController in viewControllers {
if(aViewController is ViewControllerYouWantToGoTo){
self.navigationController!.popToViewController(aViewController, animated: true);
}
}
After lots of effort I have created swift extension of back to a particular view controller in Swift 3.0.
extension UINavigationController {
func backToViewController(viewController: Swift.AnyClass) {
for element in viewControllers as Array {
if element.isKind(of: viewController) {
self.popToViewController(element, animated: true)
break
}
}
}
}
Method calling:
self.navigationController?.backToViewController(viewController: BarCodeScannerVC.self)
Here you can do this by the find the controller from the UINavigationController stack and with the help of for loop and check the condition of your desire controller and if the condition gets fulfilled it will pop to the destionation controller.
let viewControllersStack: [UIViewController] = self.navigationController!.viewControllers
for firstViewcontroller in viewControllersStack
{
if firstViewcontroller is desireViewController
{
self.navigationController!.popToViewController(firstViewcontroller, animated: true)
}
}